Optomechanical design of the DragonCam microscopic camera

TL;DR

The paper details the optomechanical design of the DragonCam microscopic camera for NASA's Dragonfly mission, emphasizing its optical configuration, focus mechanism, environmental resilience, and integration for Titan surface imaging.

Contribution

It introduces a novel optical and mechanical design tailored for Titan's surface imaging, including a tilted focal plane and focus mechanism, derived from Mars Hand Lens Imager technology.

Findings

Optical performance maintained after heating to -30C.

Designed to survive at -130C without power.

Focus merging reduces data downlink requirements.

Abstract

The DragonCam Microscopic Camera is an instrument being developed for NASA's Dragonfly mission [1] to Saturn's moon Titan. The Microscopic Camera will be body-fixed to the Dragonfly vehicle and will image the surface at a distance of about one meter (98.6 cm nominal) with a pixel scale of better than 60 microns/pixel and a nominal 52 degree angle to the Titan surface. With the 4.8 um pixel pitch of the sensor, this is a focal length of about 77.5 mm. To accommodate range variations due to vehicle pose and surface topography, the Microscopic Camera has a focus mechanism to give it a depth of field (DOF) of about 130mm. Since the Microscopic Camera's boresight is tilted by 52{\deg} off the vertical, the optical configuration has a compensating tilted focal plane, taking advantage of the Scheimpflug imaging principle. The optics are all-refractive with nine elements, a six-element stationary group and a three-element moving group. A plano-plano window seals the optics from the environment and also serves as the substrate for a bandpass filter. The optomechanical system is derived from the Mars Hand Lens Imager [11]; the moving group is mounted to a linear slide which is translated via a cam follower by the rotation of a cam driven by a stepper motor. The Microscopic Camera is designed to survive at temperatures as low as -130C without power. The camera is enclosed in a cavity in the foam insulation covering the spacecraft and looking through a single-pane window. Prior to imaging, the camera will be heated to operating temperature (nominal -30C) for proper actuation of the mechanism. STOP analysis has been performed to demonstrate that optical performance is maintained after heating. Software focus merging will be performed in the onboard camera control electronics to minimize image data downlink requirements.